Welcome from Indiana, that is a nice looking truck. There is another ground from the frame to the cab underneath. Connectors can get corroded at the plug, and that causes an intermittent short.
The Body Control Module under the dash. The other sensor is the ambient light sensor in the dash, though that shows up if the lights in the cluster get dark.
I should get the vac out and go after mine.
The articles are tough. I worked at the factories making autoparts, all that when I was younger. Time and tide waits for no man.
There is a adjuster on the top of the box, 17mm wrench, and hex allen key, try loosening it like an 1/8th of a turn to see if you get play back in your steering.
I'm jealous, I had a shop where I could keep them stashed, though my wife would tease me about the monthly bill from the BMV. That C3, shortbed 99, and K10 are 100% what I like: cruiser, daily, and woods truck all neatly tied up.